Process and device for supplying processing gas to a reactor located in a zone subjected to intense electric and/or electromagnetic fields

ABSTRACT

The device described serves to supply processing gas to an ionic implanter isolated from its environment by an electrically conductive enclosure connected to earth. Said gases are supplied by intermediate containers arranged permanently inside the enclosure and periodically filled from gas sources arranged outside, via pipelines which are at least partly insulated and pass through the enclosure. Each phase of filling the containers which is effected during the periods when the implanter is stopped, is followed by a gas evacuation phase through said pipelines. The invention overcomes the problems relating to the replacement of gas cylinders arranged around the enclosure in conventional installations.

BACKGROUND OF THE INVENTION

The invention relates to a process and device for supplying processinggas to a reactor located in a zone subjected to intense electric and/orelectromagnetic fields likely to cause ionization of said gas.

It applies more particularly, but not exclusively, to supplying aprocessing device with processing gas by ionic bombardment, for examplean ionic implanter of the type used in the semiconductor industry forincorporating ionized chemical species on silicon substrates for dopingthereof.

In this example, the generation, acceleration and focussing of the ionsbring into play considerable electric fields, requiring voltage sourcesof several tens of kilovolts.

This is why, for safety reasons, the reactor (or ionization chamber) inwhich the processing takes place is isolated, as well as the elementsbrought to said voltages situated in its environment, in a conductingenclosure serving as electric and/or electromagnetic screen which formsa potential barrier between its inner volume and its outer environment.

Because of the intensity of the intense electric fields present insidethe enclosure, it is impossible during processing to admit theprocessing gases into the ionization chamber from gas sources situatedoutside the enclosure, particularly because of:

the impossibility of passing the metal pipelines through the enclosure(even in the case where these pipelines are sufficiently isolated withrespect to the enclosure, these pipelines would be brought to highpotentials and would form electric conducting bridges between the innervolume of the enclosure and its outer environment,

the impossibility of causing the gases to flow through non conductingpipelines, because such gases would be ionized and would becomeconducting.

Considering these problems, the present solution consists in usingprocessing gas reserves of small capacity (0.6 l in general) placed in aventilated metal box, itself disposed inside the conducting enclosureand brought to the same potential as that of a high voltage source whichsupplies the reactor.

This solution has however several major drawbacks:

the need to frequently replace the cylinders, such replacement involvingopening the conducting enclosure after interrupting the high voltagesupply and after making sure that no residual electric charges remaininside the enclosure, these operations only being able to be carried outduring a prolonged shut-down of the reactor;

handling difficulties due in particular to the compactness of theexpansion panel associated with the gas sources and its position insidethe enclosure, and

a risk of contamination and corrosion of the equipment situated insidethe enclosure during handling, such equipment being furthermore veryexpensive.

OBJECT AND SUMMARY OF THE INVENTION

The invention has then particularly as object to overcome all thesedrawbacks.

It proposes generally a process for supplying, with processing gas, areactor operating by means of a high voltage current and situated in azone subjected to intense electric and/or electromagnetic fields likelyto cause ionization of said gas, said zone being insulated electricallyfrom its outer environment by at least one electrically conducting wallforming a potential barrier.

According to the invention, this process is more particularlycharacterized in that it consists in supplying said reactor with gas bymeans of at least one intermediate capacity filled periodically from agas source situated outside said zone, during interruptions of the highvoltage current, by means of at least one pipeline passing through thewall, this pipeline being made from an electrically insulating materialat least on its portion passing through said wall.

Furthermore, each phase of filling the intermediate capacity will befollowed by closure of said pipeline in a portion situated in said zone,and evacuation of said gas at least in a portion of said pipelinepassing through said wall.

Advantageously, such removal will be carried out by scavenging saidportion with a gas which is not ionizable by said fields.

Considering the complete electric insulation provided by theelectrically insulating material portion of the pipeline and because ofsaid evacuation of the processing gas, at least in this portion, theintermediate capacity may be advantageously brought to a high voltage,like the gas reserves used previously.

BRIEF DESCRIPTION OF THE DRAWINGS

Of course, the invention also relates to the devices for implementingthe above defined process.

One embodiment of such a device will be described hereafter by way ofnon limitative example with reference to the accompanying drawings inwhich:

The single FIGURE is a schematic representation of a device forsupplying, with processing gas, an installation capable of effectingionic implantations on semiconductor wafers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In this installation the ionic implanter 1 (shown schematically by ablock) is enclosed with its high voltage supply 2 inside an enclosure 3made from an electrically conducting material connected to earth.

This enclosure 3 therefore provides electric and electromagneticinsulation, by means of a potential barrier, between its inner volumeand its outer environment.

The processing gas supply for the ionic implanter 1 is provided by abattery of intermediate capacities C₁, C₂ (only two of which have beenshown) disposed permanently inside enclosure 3 and whose inlet andoutlet pipes are equipped with remotely controllable valves 4, 5-4', 5',for example pneumatically controlled valves, whose control circuits 6(for example the intake pipes and possibly compressed air outlet) madeat least partially from electrically insulating materials, pass throughthe enclosure to reach a control station 7. In this FIGURE, such controlcircuits have been grouped together in a single bundle shown with finelines. These controllable valves 4, 5-4', 5' are further equipped withsensors for detecting their state (open, closed), such sensors beingconnected to the control station, for example by optical fibreconnections 8 which pass through the enclosure. Here, also for the sakeof clarity, such connections have been grouped together in a singlebundle shown with a fine line.

The output pipes from the intermediate capacities C₁, C₂ are connecteddownstream of valves 4, 4' to a common collector 9 connected to theprocessing gas intake pipe of the ionic implanter 1.

The input pipes of capacities C₁ , C₂ are connected to processing gascylinders 10, 11 located outside the enclosure 3 by intake circuits eachcomprising, upstream of valves 5, 5':

means 12, 12' for connecting a scavenging circuit whose purpose will bedescribed hereafter,

a duct section 14, 14' made from an electrically insulating material,situated in a zone of this circuit passing through enclosure 3,

a vent orifice 15, 15' which can be closed by a controlled valve 16,16', and

a processing gas intake control valve 17, 17' located at the outlet ofcylinder 10, 11 (this valve being possibly incorporated with thecylinder 10, 11).

In this example, the scavenging circuit comprises a pressurized neutralgas source 18, for example a compressed argon generator, situatedoutside enclosure 3 whose outlet pipe equipped with a valve 20 passesthrough enclosure 3 through an electrically insulating material section21 for connection to the connection means 12, 12', by means ofconnecting pipes each equipped with a remotely controllable valve 22,22'.

These valves 22, 22' are controlled by means of control circuits similarto those of valves 4, 5 - 4', 5' which pass through the enclosure forconnection to the control station 7.

Similarly, the state of these valves may be detected and transmitted tothe control station 7 by an optical fibre transmission system.

A similar transmission system may further be used for transmittinginformation relative to the pressure of the gases contained in theintermediate capacities C₁, C₂ and which comes from pressure sensors 23,23' specially designed for this purpose.

To avoid electrostatic or electrodynamic phenomena due to the presenceinside the enclosure of intense electric fields, the intermediatecapacities C₁, C₂ are brought to the high voltage potential of supply 2.

In accordance with the process of the invention, the intermediatecapacities C₁, C₂ are filled during interruptions of the high voltagegenerated by the supply 2, for example before start-up and/or theimplantation phases carried out by the ionic implanter 1.

Each such filling involves previously the closure of valves 4, 4', ofthe vent valves 16, 16' and of the scavenging valves 22, 22' thenopening of valves 5, 5' and 17, 17'.

The processing gas from cylinders 10, 11 is then injected into theintermediate capacities C₁, C₂ until the pressure therein reaches apre-determined threshold. At that time the pressure sensors 23, 23'transmit to the control station 7 an end of filling signal. The latterthen outputs a control signal for closing the valves 5, 5' and 17, 17',then triggers off the scavenging phase.

This scavenging phase is then obtained by opening valves 22, 22' and 20and the vent valves 16, 16'.

Following such opening, the compressed argon generated by source 18 isinjected into the intake circuits just upstream of valves 5, 5'. Thiscompressed gas will flow in an opposite direction through the intakecircuits and drive the processing gases through the vent orifice 15,15'. Once this scavenging phase has been carried out, the controlstation will cause closure of valves 22, 22', 16, 16' and 20.

The high voltage may be re-established for carrying out an implantationphase, the processing gas then being admitted into the ionic implanterfollowing opening of valves 4, 4'.

Because of the electrically insulating material sections and because thegas contained therein is not ionizable by the high voltage delivered bythe generator, no transfer of electric energy can occur between theinner volume of the enclosure and its outer environment.

The safety of this device may be increased by providing a device forpreventing opening of valves 17, 17' and 5, 5' and, consequently, anypossibility of access of the processing gas to the sections 14, 14'during the periods of application of the high voltage.

I claim:
 1. Process for supplying, with processing gas, a reactoroperating by means of a high voltage current and situated in a zonesubjected to intense electric and/or electromagnetic fields likely tocause ionization of said gas, said zone being insulated electricallyfrom its outer environment by at least one electrically conducting wallforming a potential barrier, said process consisting in supplying saidreactor with gas by means of at least one intermediate container filledperiodically during filling phases from a gas source situated outsidesaid zone, during interruptions of the high voltage current, by means ofat least one pipeline passing through the wall, this pipeline being madefrom an electrically insulating material at least in a portion passingthrough said wall and in that each of said filling phases is followed byclosure of said pipeline by closure means situated in said zone, andevacuation of said gas at least in said portion.
 2. Process according toclaim 1, wherein said evacuation is carried out by scavenging saidportion with a gas which is not ionizable by said fields.
 3. Processaccording to claim 1, wherein said reactor is an ionic implanter. 4.Device for supplying, with processing gas, a reactor operating by meansof a high voltage current and situated in a zone subjected to intenseelectric and/or electromagnetic fields likely to cause ionization ofsaid gas, said zone being insulated electrically from its outerenvironment by at least one electrically conducting wall forming apotential barrier, said device further comprising at least oneintermediate container disposed permanently inside said zone, saidcontainer having an output connected to a processing gas intake pipe ofthe reactor through a pipeline equipped with a first valve which can becontrolled from the outside and an input, connected to a processing gassource situated outside through an intake pipe comprising, in said zone,a second valve which can be controlled from outside, a section made froman electrically insulating material which extends through at least theportion of the circuit passing through said wall and, in its partexternal to said zone, a vent orifice equipped with a controllableclosure means then a valve controlling the intake of the processing gas,said device further comprising a scavenging circuit having, outside saidzone, a source of gas which is not ionizable under the effect of saidfields connected to the processing gas intake circuit at a positionsituated in said zone, upstream of the second valve through a scavengingpipe passing through said wall.
 5. Device according to claim 4, whereinsaid scavenigng pipe comprises at least a third valve situated insidesaid zone and controllable from outside.
 6. Device according to claim 4,wherein at least one section of the scavenging pipe passing through saidwall is made from an electrically insulating material.
 7. Deviceaccording to claim 4, wherein the state (open or closed) of said first,second and third valves is detected by respective sensors connected to acontrol station outside said zone by transmission lines passing throughsaid wall.
 8. Device according to claim 7, wherein said transmissionlines are of optical fibre type.
 9. Device according to claim 4, whereinsaid intermediate container is equipped with pressure sensors adaptedfor transmitting an end of filling signal to a control station situatedoutside said zone.